Drinking flask



FIG. 1 is a top, front and left side perspective view of a drinking flask showing our new design;

FIG. 2 is a bottom, front and right side perspective view thereof;

FIG. 3 is a top plan view thereof;

FIG. 4 is a bottom plan view thereof;

FIG. 5 is a front elevation view thereof;

FIG. 6 is a rear elevation view thereof; and,

FIG. 7 left side elevation view, the right side elevation being a mirror image thereof.

The broken lines in the drawings depict environmental subject matter only and form no part of the claimed design. 

CLAIM The ornamental design for a drinking flask, as shown and described. 